1. Field of the Invention
The present invention relates to the field of magnetic pump drives and, more particularly, to a magnetic pump drive comprising an isolating shell. In particular the magnetic pump drive comprises a driver/ driven by a motor, a rotor encircled by the driver and connected with an impeller of the pump, at least two circles of permanent magnets, one of the two circles being attached to a cylindrical face of the rotor and respectively the driver in opposite relation, and a stationary isolation shell. The stationary isolation shell, which encircles the rotor, is filled by the medium to be pumped and is sealed against the housing of the pump. The force of the permanent magnets passes through the isolating shell for effecting the drive from the driver to the rotor.
2. Description of the Prior Art
Magnetic pump drives have been known in the art for many years. The known drives have proven to be reliable in the chemical industry and in nuclear power stations. Because there is no shaft duct and there is no leakage along a shaft out of the sealing, these pumps have only gaskets, which are more easily handled and which are much less prone to a leak than a seal against a rotating shaft.
When a pump of this kind is submitted to high system pressures, the isolating shell has the tendency to bulge, i.e. to take the form of a barrel. This tendency is even greater when a rather strong drive is necessary so that several circles of single permanent magnets are used, one after the other, in order to transmit the required torque in the drive section. In this case the free length between the sealing flange of the isolating shell and its bottom is rather large so that the biggest increases in diameter due to high system pressures occur in the middle section of the isolation shell.
It has been tried to prevent corresponding deformations of pumps made completely from plastic material by winding fibres onto the isolating shell which consists also of a plastic material. The fibres are formed onto the isolating shell in a slightly pre-biased condition in order to allow a certain deformation under load.
The aim of these intentions is to arrange the permanent magnets of the driver and rotor at a distance from one another as small as possible for achieving a good efficiency of the permanent magnetic clutch. Thus a rather small thickness of the isolating shell at least in the cylindrical section and a small deformation due to pressure loads are practically achieved so that losses in efficiency are not too great when, for safety reasons, a greater distance between opposing magnets is chosen than necessary as a matter of design choice.
When metallic isolating shells are used, the gains, as to form stability by fibres wound onto the cylindrical sections, are small, since nearly the same effect is achieved by a direct thickening of the isolating shell wall. The drop in efficiency is accepted.
In co-pending German patent application P36 12 802.3 filed Apr. 16, 1986 and published Oct. 22, 1987, the present applicant has proposed to support the cylindrical section of the isolating shell by rings between which the circles of permanent magnets are arranged. Thus the form stability of the isolating shell is enhanced; however, the assembly is rather complicated. It is necessary to use a driver made from two halves or to take corresponding measures.